Activator solutions, their preparation, and use in electroless plating of surfaces

ABSTRACT

Surfaces intended to be electrolessly metal plated, for instance the surfaces of through holes of through hole printed circuit boards, are treated with a colloidal catalyst metal-free acid liquid solution of a soluble, lower alkanolmodified noble metaltin chloride complex until the surface is rendered catalytic. The noble metal of the complex is a noble metal which is catalytic to the deposition of the metal destined to be electrolessly plated on the surface.

United States Patent [191 Fadgen, Jr. et al.

Mar. 18, 1975 ACTIVATOR SOLUTIONS, THEIR PREPARATION, AND USE INELECTROLESS PLATING OF SURFACES [75] Inventors: Earl J. Fadgen, Jr.,Clinton; Juan Hajdu, Orange, both of Conn.

[73] Assignee: Enthone, Inc., West Haven, Conn.

[22] Filed: Oct. 29, 1973 [21] Appl. No.: 410,645'

[52] US. Cl. 106/1 [51] Int. Cl. C23c 3/00 [58] Field of Search 106/1;252/794 Primary 'E.raminerLewis T. Jacobs Attomy, Agent, or Firm-RogerJ. Drew; Elwood .l. Schaffer [57 ABSTRACT Surfaces intended to beelectrolessly metal plated. for instance the surfaces of through holesof through hole printed circuit boards, are treated with a colloidalcatalyst metal-free acid liquid solution of a soluble, loweralkanolmodified noble metal-tin chloride complex until the surface isrendered catalytic. The noble metal of the complex is a noble metalwhich is catalytic to the deposition of the metal destined to beelectrolessly plated on the surface.

35 Claims, N0 Drawings AND USE IN ELECTROLESS PLATINGfOE SURFACES H h tBACKGROUND OF THE INVENTION 1. Field of the Invention 1 This inventionrelates to electroless-m" 'tal plating and more particularly to aprocess for tlie chemical reduction deposition of metal coatings onsurfaces involving a new and improved catalytic-activation of thesurface or surfaces prior to the chemical reduction metal deposition.Additionally this invention relates to new and improved catalystsolutions which are substantially free of collodial metal particles, andto a method for preparing the catalyst solutions. .7 2. Description ofthe Prior Art Prior activation systems for electroless metal depositionconsisted of separate solutions of a stannous salt,

used heretofor for activation substrates for electroless metal plating.The colloidal activation or catalyst systems referred to above, althoughgiving good results in certain respects, leave room for improvement fromthe standpoint of stability of the colloidal catalystcontaining bathsand effectiveness in catalyzing the surface or surfaces intended to beelectrolessly metal plated. Thus the colloidal activator or catalystsystem have colloidal catalyst particles of such large size thatcontacting and catalyzing of certain surface or surfaces intended to beelectrolessly metal plated tends to be impossible, for example inpenetrating, contacting and activating the surfaces of narrow, deeprecesses such as those often found in multi-layer printed circuit'boardsand the surfaces of small holes, especially small blind holes, andcrevices encountered in plating other plastics.

U.S. Pat. No. 3,011,920 discloses the use of a liquid containingcolloidal particles of the catalytic metal dispersed therein foractivating a surface for electroless deposition of metal thereon. Thecolloidal catalyst sol is obtained by admixing a noble metal salt, a tinsalt, and a hydro-halide acid. Although the colloidal catalyst sol givessatisfactory results foractivation, the colloidal catalyst sol leaveappreciable room for improvement in activating the surfaces of printedcircuit boards, due to the colloidal catalyst particles being of suchlarge size as to prevent the particles from penetrating and hencecontacting and activating the surfaces of the narrow, deep recesses. Thecolloidal catalyst sol of U.S. Pat.

' No. 3,01 L920 also leaves room for improvement from the standpoint ofinherent stability of the catalyst or activator composition.

The colloidal catalyst sols and baths of the prior art also leave roomfor improvement with regard tolerance to dragged in CrO and HSO.,containing aqueous conditioner solution. The plastisol-coated platedracks employed in the plating cycle tend to have TNT: aftei' 'the' racksare older and have been in use for an apcracks, fissures and pores inthe plastisol, especially preciable time, and the conditioning solutionmay be retained in the cracks, fissures and pores and consequentlydragged in to the activator bath despite water rinsing after theconditioning and prior to immersion of the racked articles to be platedinto the activator bath. The presence of the dragged in CrO and H SOcontaining conditioner solution in the prior colloidal catalyst sols andbaths may result in a premature or quite early decomposition of thecolloidal catalyst or activator sol to the extent that it will no longerfunction to effectively catalyze the article surface or surfaces to beelectrolessly metal plated.

Moreover, use of the colloidal cataylst sol of U.S. Pat. No. 3,01 1,920in the plating cycle requires a special post-activation treatment of thecatalyzed article surface or surfaces with a post-activation solutionwhich may be hazardous as hereafter disclosed, to remove protectivecolloid and/or deflocculating agent from the deposited colloidalcatalytic metal particles. The post-activation solution employed forthis special post-activation treatment may contain perchloric acid, andsuch post-activator solution could present an explosion and fire hazarddue to the perchloric acid undergoing a spontaneous and explosivedecomposition under certain conditions.

Catalyst solutions containing a soluble Lewis basemodified noblemetal-tin halide complex and free or substantially free of colloidalcatalyst metal are disclosed and claimed in U.S. Pat. No. 3,767,583,assigned to the common assigne e. Although such catalyst solutions ofUS. Pat. No. 3,767,583 constitute an improvement in certain respectsover the colloidal catalyst sol of the prior art for catlyzing surfacesdestined to be electrolessly metal plated and are eminently suited foruse in plating on plastics generally, the catalyst solutions of U.S.Pat. No. 3,767,583 leave room for improvement in catalyzing the walls ofthe through holes of through hole printed circuit boards and ofmulti-layer printed circuit boards. A portion or portions of the surfacearea of the through hole walls were usually not activated using thecatalyst solution of U.S. Pat. No. 3,767,583, and consequently thesenon-activated surface portions of the through walls were not metalplated and hence not rendered electrically conductive during thesubsequent electroless metal plating step.

BRIEF SUMMARY OF THE INVENTION It has now been found in accordance withthe present invention that by aclose control of the molar ratio ofstannous chloride to noble metal chloride utilized in the preparation ofthe soluble lower alkanol-modified noble metal-tin halide complexdisclosd in the aforementioned U.S. Pat. No. 3,767,583; as well as byutilizing higher reaction temperatures in the preparation of suchalkanol-modified noble metal-tin halide complex than was utilized in thepreparation of the complexes of aforementioned U.S. Pat. No. 3,767,5 83,catalyst solutions containing a soluble lower alkanol-modified noblemetal-tin chloride complex are obtained which are especially welladapted for catalyzing for chemical reduction metal plating the walls ofthrough-holes of both single layer and multi-layer printed circuitboards. Additionally the catalyst solutions of this invention are welladapted for catalyzing the surfaces of other plastics for chemicalreduction metal plating, and are stable catalyst solutions. The molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) utilized in the preparation of the catalystsolutions herein should intially be at least abut 9-l0zl of stannouschloride to noble metal chloride (calculated as palladium chloride)respectively, and the reaction temperature should be about l60F. orhigher but below that temperature at which an excessive amount of noblemetal is precipitated. By Excessive amount of noble metal beingprecipitated as used herein is meant the precipitation from solution ofmore than percent by weight of the noble metal. By lower alkanol as usedherein is meant a l-4C inclusive alkanol singly or a mixture of two ormore 14C alkanols The catalyst solutions of this invention are preparedby mixing together the lower alkanol, the soluble noble metal chloride,stannous chloride and hydorchloric acid, and maintaining thethus-obtained liquid mixture at a reaction temperature of at least about160F. but below that temperature at which an excessive amount of noblemetal is precipitated for a time sufficient to obtain the soluble loweralkanol-modified noble metaltin chloride complex. The stannous chlorideis present in the reaction mixture in excess of the amount thereofrequired to reduce the noble metal chloride to zero valent noble metaland the lower alkanol is present in the reaction mixture in amountsufficient to obtain a soluble complex. The initial molar ratio ofstannous chloride to noble metal chloride (calculated as palladiumchloride) is essentially about 9-l0:l or higher respectively. Thecatalyst solution of this invention usually has a pH less than 1.

The minimum ratio of stannous chloride to noble metal chloride(calculated as palladium chloride) of about 9-lO:l respectively iscritical herein for the reasons that at a molar ratio of stannouschloride to noble metal chloride (calculated as palladium chloride)appreciably below 9lO:l respectively, a material portion of the reactionproduct complex will precipitate from the solution. This is undesirableand uneconomical because the noble metal of the precipitated complex isno longer available as catalyst for activating nonconductive surfacesfor chemical reduction metal plating, for instance the walls of throughholes of single layer and multi-layer printed circuit boards. The upperlimit of the molar ratio of stannous chloride to noble metal chloride(calculated as palladium chloride), is not especially critical and canbe varied over a wide range.

The minimum reaction temperature of about 160F. is critical for thereason at reaction temperatures much below l6()F. the resultant catalystsolutions containing a soluble lower alkanol-modified palladium-tincomplex are not sufficiently catalytic to ensure complete chemicalreduction metal plating the walls of throughholes of both single andmulti-layer printed circuit boards.

The period of maintaining the reaction mixture at the temperature ofabout 160F. or higher to obtain the soluble lower alkanol-modified noblemetal-tin chloride complex herein is a non-lengthy period as comparedwith the plural day holding period of the preparation method of U.S.Pat. No. 3,767,583, and i s at least about 1 hours in duration andsufficient to obtain the soluble complex.

In another embodiment of the invention and which is a preferredembodiment, the lower alkanol is supplied to the reaction mixture inamount which is sufficient to obtain the soluble alkanol-modified noblemetal-tin chloride complex, but which is an insufficient amount of thelower alkanol to result in excessive gas pressure build-up in themarketing or transporting closed con tainer for such complex. Byeliminating excessive gas pressure building up in the closed marketingcontainers, venting of the containers required with the catalystsolutions disclosed and claimed in the aforementioned U.S. Pat. No.3,767,583 is no longer required. Furthermore, the elimination of theexcessive gas pressure build-up enables the catalyst solutions of thisinvention to be shipped by air, which could not be done with thecatalyst solutions of aforementioned U.S. Pat. Nov 3,767,583.

The noble metal of the complex is a noble metal that is catalytic to theelectroless, i.e. chemical reduction, metal plating of the particularmetal or metals in the case of alloy plating, destined to beelectrolessly plated on the surface or surfaces. The treatment of thesurface or surfaces with the solution of soluble loweralkanolmodified-noble metal-tin halide complex is usually by immersingthe surface or surfaces in the solution, although any other suitablemeans of applying the solution onto the surface or surfaces could beutilized, if desired. The thus-obtained catalytically active surface isthen electrolessly metal plated to deposit or plate the desired metal ormetals on the treated surface or surfaces.

The catalyst solution of the present invention is a colloidal catalystmetal particle-free acid liquid solution containing a soluble loweralkanol-modified noble metal-tin chloride complex. The catalyst solutioncan be a concentrate solution or a concentrate solution which hasdiluted with an aqueous liquid, usually water, and a hydrogen halideacid, such as hydrochloric acid, prior to use.

The formation of the soluble lower alkanol-modified noble metal-tinchloride complex of this invention is indicated when the resulting acidsolution of the reaction product either as such or when diluted ashereafter disclosed, is catalytically effective for catalyzing theobject surface or surfaces to be electrolessly metal plated. By suchterm catalytically effective" is meant the acid solution as such or whendiluted as hereafter disclosed of the soluble lower alkanol-modificdcomplex of this invention will convert an otherwise noncatalytic orsubstantially non-catalytic object surface or surfaces intended to beelectrolessly metal plated into a catalytic surface or surfaces, uponimmersion of the non-catalytic surface or surfaces therein for asufficient immersion time as is hereinafter disclosed, which will resultin a satisfactory metal plate or deposit being deposited on thethus-obtained catalytic surface or surfaces upon immersion of suchcatalytic surface or surfaces in an electroless or chemical reductionmetal plating bath, for instance a chemical reduction copper or nickelplating bath, for a time sufficient to deposit the metal on thecatalytic surface.

The thus-obtained solution of the lower alkanolmodified noble metal-tinchloride complex in the hydro-halide acid is utilizable as such as anactivator for catalyzing the article surface or surfaces to beelectrolessly metal plated. However, for economic reasons we recommenddillution of such acid solution, which is a concentrate solution, priorr0 use, for instance by mixing together, by volume, 2 parts of suchconcentrate solution, 1 part of HCl (Analytic Reagent grade) of 37% HClconcentration, and 5 parts of deionized or distilled water.

The lower alkanol is essential for forming the soluble complex hereininasmuch as in the absence of the lower alkanol a soluble complex is notobtained and instead a colloidal sol is formed. Thus when a loweralkanol was omitted in the preparation of the complex, insoluble,collodial catalyst particles and a colloidal sol was obtained.

Although we do not wish to be bound by theory, it is believed that themechanism involved in the formation of the soluble loweralkanol-modified noble metal-tin halide complex herein is an initialacid-catalyzed reduction of the ionic noble metal by the stannouschloride to zero valent noble metal. The lower alkanol, e.g. methanol,then forms a complex or coordination compound with the noble metal andstannous chloride. A molecular rearrangement or ligand transfersubsequently occurs which is inhibited by the lower alkanol quiteprobably due to steric blocking mechanisms. The soluble complex moleculeformed is ionic and specifically anionic. It is further believed thatthe higher reaction temperature employed in preparing the soluble.

complex herein results in an increased yield of catalytically activespecies of complex over catalytically inactive species, by reason of thereaction or reactions not stopping at intermediate inactive species asmuch as apparently occurs at the lower reaction temperatures of US. Pat.No. 3,767,583. This is believed to explain at least in part theconsiderable improvement of the catalyst solutions of this inventionover those of US. Pat. No. 3,767,583 for catalyzing the through holewall surfaces of single layer and multi-layer printed circuit boards.

The 1-4 C alkanols herein include methanol, ethanol, isopropanol,n-propanol and n-butanol. So far as we are aware, any soluble noblemetal chloride is utilizable herein. Exemplary of noble metal chloridesutilizable herein are chlorides of platinum group metals, e.g. palladiumchloride, platinum chloride and aurous chloride. Chlorides of otherplatinum group metals utilizable herein are chlorides of rhodium,ruthenium, os-

. mium and irridium dichloride, osmium trichloride, rhodium trichlorideand ruthenium tetrachloride. The particular soluble noble metal chlorideutilized of course will correspond to the particular noble metal desiredin the complex.

The lower alkanol should be present in the reaction mixture at theoutset of the redox reaction between the stannous chloride and noblemetal chloride, to prevent the formation of an insoluble, relativelyhigh molecular weight colloidal system and the precipitating out of zerovalent noble metal.

The activator concentrate solutions and diluted concentrate solutionsare acid solutions and usually have a pH below about 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred lower alkanol ismethanol.

The preferred reaction temperature for forming the loweralkanol-modified noble metal-tin chloride complex is in the range ofabout 160F. to about 185F. More preferably, the reaction temperature isin the range of about 170F. to about 185F.

The preferred period of maintaining the reaction mixture at thetemperature of F. or higher is at least about 4-9 hours and sufficientto obtain the soluble lower alkanol-modified-noble metal-stannouschloride complex, more preferably about 9 hours and suffi cient toobtain the soluble complex.

Preferably, as the reaction temperature is increased, the molar ratio ofstannous chloride to noble metal chloride (calculated as palladiumchloride) is increased in preparing the catalyst solution of thisinvention. Thus at areaction temperature of l60F. up to l70F., the molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) is preferably in the range of about 9.0-l0.0:lrespectively; at a reaction temperature of F. to F., the molar ratio ofstannous chloride to noble metal chloride (calculated as palladiumchloride) is preferably in the range of about 9.5l0.5:l respectively; ata reaction temperature of 175F. to F. the molar ratio of stannous.chloride to noble metal chloride (calculated as palladium chloride) ispreferably in the molar ratio range of about 110-] 1.721 respectively;and at a reaction temperature of 180F. to F., the molar ratio ofstannous chloride to noble metal chloride (calculated as palladiumchloride) is preferably in the molar ratio range of about 1 l.7-l2.0:lrespectively.

The lower alkanol is preferably added in the formation of .the reactionmixture before addition of the acidsoluble noble metal chloride. If thelower alkanol is not present at the outset of the redox reaction betweenthe stannous chloride and noble metal chloride, this redox reaction,which occurs rapidly, may result in the zero valent noble metalresulting from the redox reaction .either forming an insoluble,relatively high molecular weight colloidal system and/or precipitatingout.

The lower alkanol is preferably added to the reaction mixture in amountin the range of about 0.52.5% by volume (based on total reactionmixture).

The soluble stannous chloride reactant is preferably added to thereaction mixture in the preparation of the soluble loweralkanol-modified noble metal-tin chloride complex herein in increments,for instance three or four or more increments, with mixing of theresulting mixture between the increment additions. The watersolublestannous chloride is preferably in solution in an aqueous hydorchloricacid solution for each increment addition. An amount of stannouschloride is preferably added in the first incremental addition which isin excess of the amount stoichiometrically required to reduce all noblemetal salt to zero valent noble metal. The additional incrementaladditions of the soluble stannous chloride are sufficient in size andnumber to provide an amount of stannous halide in the reaction mixturewhich is sufficient to apparently slowly promote a slight increase inmolecular size of the complex to a species capable of catalyzing thechemical reduction deposition of a metal or metals to be electrolesslyplated. The temperature of the reaction mixture during the mixingbetween the incremental additions of stannous chloride is preferably inthe range of about 160F. to about 185F., more preferably about 170F. toabout 185F. The reaction temperature can be maintained within suchtemperature ranges by supplemental heating from an external sourceand/or by cooling, as required.

The lower alkanol is preferably added to the reaction mixture prior tothe addition of the noble metal chloride as previously disclosed hereinand is added in amount which is at least sufficient to prevent aninsoluble relatively high molecular weight colloidal catalyst systemfrom forming and a zero valent noble metal from precipitating. I

Preferably an alkali stannate, for example an alkali metal stannate,e.g. sodium or potassium stannate, is added to the reaction mixtureprior to the addition of the stannous chloride to facilitate thereaction.

The preferred noble metal chloride reactant is palladium chloride.

The reaction medium for forming the soluble lower alkanol-modified noblemetal-tin chloride complex is an acid aqueous medium preferably of a pHbelow about I. The acid pH of the reaction mixture or medium ismaintained by the addition of hydrochloric acid.

An especially preferred method of preparing the soluble loweralkanol-modified noble metal-tin chloride complex is by introducingwater and a soluble alkali metal stannate, e.g. sodium stannate into areaction vessel or zone, and agitating or stirring the resulting mixtureuntil the alkali metal stannate is dissolved in the water. A liquidsolution containing stannous chloride and hydrochloric acid is added tothe thusobtained liquid aqueous solution and the resulting mixtureagitated or stirred for typically about 10 minutes. Hydrochloric acid isthen added to the thus-obtained liquid mixture, followed by the additionof the lower alkanol to the resulting liquid mixture. The resultingliquid mixture isheated to a reaction temperature in the range of about170F to about 185F. while agitating or stirring the same, a controlledor metered amount of a liquid solution of palladium chloride inhydrochloric acid is added to the thus-obtained liquid mixture, and asolution of stannous chloride in hydrochloric acid is added in threeincrements which are substantially equal in size and concentration tothe resulitng liquid mixture. The pH of the reaction mixture ismaintained below pH during and after the addition of the palladiumchloride solution thereto. The incremental addition of the stannouschloride solution in hydrochloric acid to the liquid mixture is usuallymade during the slow addition of the solution of palladium chloride inhydrochloric acid to the liquid mixture as disclosed immediately supra.Hydrochloric acid and stannous chloride are then separately added to thethus-obtained liquid mixture, with the stannous chloride being addedslowly to such liquid mixture. Prior to such separate additions ofhydrochloric acid and stannous chloride, the temperature of'theresulting liquid mixture is maintained at a reaction temperature in therange of about 170F. to about 185F. for a period of about 4 hours ormore and sufficient to obtain a catalytically effective solutioncontaining the soluble lower alkanol-modified noble metal-tin chloridecomplex. The liquid mixture is then agitated or stirred for about 5hours or longer, and the thus-obtained liquid mixture is cooled to roomtemperaturev without agitation ofthe mixture, i.e. in a quiescent state,preferably by being permitted to cool to room temperature. The productcatalytically effective solution containing the soluble loweralkanol-modified noble metal-tin chloride complex can be utilized orpackaged in suitable marketing drums or other suitable containers.

The agitating or stirring in the preparation method set forthimmediately supra can be effected with any suitable agitator means orstirrer.

The article or substrate surface or surfaces to be plated, if notalready clean, are cleaned, for instance by immersion in a conventionalhot non-silicated alkaline cleaner solution. However, any suitable meansof cleaning the surface can be utilized including mechanical cleaning,such as for example by sanding or abrading. The surface or surfaces arethen rinsed in water. Following the rinsing, the surface or surfaces tobe plated may then be dipped in a dilute acid solution, e.g. an aqueousHCl solution of 20% HCl concentration, to neutralize any alkalinematerial remaining, followed by water rinsing the thus-treated surfaceor sufaces.

The thus-treated substrate surface or surfaces are then catalyzed byimmersing the surface or surfaces in the colloidal metal particle-freeliquid activator solution of the soluble lower alkanol-modified noblemetaltin chloride complex of this invention and specified in Example 1for a time sufficient to render the surface or surfaces catalyticallyactive, usually a time of 1 minute or more. Alternatively and lesspreferably such solution of soluble lower alkanol-modified noblemetal-tin chloride complex can be sprayed onto the surface or surfacesto be catalyzed. The thus-obtained catalyzed surface or surfaces arethen withdrawn from the activator or catalyst solution and ordinarilyrinsed in water.

The catalyzed surface or surfaces are then ordinarily contacted with,usually by immersing in, a postactivation solution, preferably a dilutesolution of HCl (10-25% HCl concentration), for a contact time which issufficient to assure exposure of catalytic noble metal on the surface orsurfaces, usuallyl minute or longer,

followed by ordinarily rinsing in water. The contacting with thepost-activation assures exposure of the catalytic noble metal 'on thesurface or surfaces.

Any solution capable of assuring exposure of the catalytic noble metalon the surface or surfaces to be electrolessly metal plated can beutilized as the postactivation solution, although the dilute HClsolution is preferred as previously disclosed herein. Although we do notwish to be bound by theory, it is believed that the post-activationsolution treatment functions to remove material such as, for instance,excess tin from the treated surface or surfaces thereby exposingcatalytic noble metal. However another explanation advanced is that thepost-activation solution treatment renders material other than thecatalytic noble metal on the treated surface or surfaces incapable ofdetrimentally interfering with the catalytic activity of the noblemetal.

The catalytic surface or surfaces are then electrolessly metal plated bycontacting the catalyzed surface or surfaces, usually by immersing suchsurface or surfaces in, a chemical reduction metal plating solution forplating the desired metal, for example a chemical reduction copperplating solution, a chemical reduction nickel plating solution, achemical reduction cobalt plating solution, or a chemicalreductioncobalt-nickel plating bath for depositing cobalt-nickel alloys.The catalyzed surface or surfaces is contacted with the chemicalreduction metal plating solution until a metal plate or layer of thedesired thickness is deposited on the surface or surfaces. Thethus-plated surface or surfaces are then rinsed with water. Exemplary ofthe chemical reduction aqueous metal plating baths are the copper,nickel, cobalt and cobalt-nickel plating baths which follow:

Chemical Reduction Copper Plating Bath g/l Copper sulfate 29 Sodiumcarbonate 25 Rochelle salt 140 Versene T 17 Sodium hydroxide 40Formaldehyde (37% solution) l66 Versene T is a trademarked materialobtained in commerce and cotaining EDTA and triethanolamine. The bath isoperated at a bath temperature of 70F. and has a pH before plating of11.5.

Chemical Reduction Nickel Plating Bath Nickel chloride 30 Sodium citrate20 Ammonium chloride 50 Sodium hypophosphite l0 Ammonium hydroxide ThepH of the bath is adjusted to 8-10 with NH OH, and the bath is operatedat a bath temperature of 70-l 10F.

Chemical Reduction Cobalt Plating Bath g/l Cobalt chloride 30 Sodiumcitrate Ammonium chloride Sodium hypophosphite 20 The pH of the bath isadjusted to 9l0 with ammonia, and the bath is operated at a temperatureof l95-205F.

Chemical Reduction Cobalt-Nickel Plating Bath g/l Cobalt chloride 30Nickel chloride 30 Rochelle salt 200 Ammonium chloride 50 Sodiumhypophosphite 20 The pH of the bath is adjusted to 8-10 with ammonia andthe bath is operated at a temperature of l95205F.

After the electroless plating is completed, the substrate surface orsurfaces are usually then elecotroplated with the desired metal, forexample, copper. A typical electroplating bath for this purpose is anacid sulfate aqueous bath containing 100-300 g/l of Cu- SO .5H O and15-40 g/l of free H SO, (66Be). An additional metal or metals can thenbe electroplated over such electroplate layer, if desired.

The following examples are given by way of illustration but not by wayof limitation:

EXAMPLE 1 Two-hundered and eighty-nine and four-tenth (289.4) lbs. ofdistilled water was introduced into a tank equipped with a stirrer and aTeflon steam coil. With the agitator turned on, 1410.3 grams of sodiumstannate was added to the water in the tank and stirred until dissolved.75.22 lbs. of an addition solution containing 29.76% of stannouschloride and 70.24% of hydrochloric acid (A R grade) were then added tothe resulting solution and the thus-obtained solution stirred for 10minutes. 363.22 lbs. of hydrochloric acid (A R grade) was then added tothe resulting solution, after which the temperature controller was setto 170F. and the steam for heating then turned on. 7070 mls. of methanol(A R grade) was then added to the resulting solution in the tank whileheating and stirring the solution. The heating and stirring of thesolution in the tank was continued until the temperature of the solutionreached 170F. Addition of a palladium chloride solution to thethus-obtained solution in this tank was then begun with use of ametering pump, with the metering pump adjusted for 3 gallons per hour.The palladium chloride solution contained, by weight, 0.30% of palladiumchloride and 99.70% of hydrochloric acid (A R grade). At 1 hour, 2 hoursand 3 hours after beginning the addition of the palladium chloridesolution, a separate increment 20.8 lbs. in size of a stannous chloridesolution containing, by weight, about 30% of stannous chloride and ofhydrochloric acid (A R grade) was added to the thus-obtained solution.At four hours after beginning the addition of the palladium chloridesolution, 246.6 lbs. of hydrochloric acid (A R grade) was added to theresulting solution and 82.7 lbs. of stannous chloride was separately andslowly added to the resulting solution. Stirring of the solution wascontinued for 5 hours, after which the stirrer and heat was shut off.The thus-obtained liquid mixture was held in the tank overnight, and thenext morning stirred for 15 minutes and then packaged.

The thus-obtained liquid solution containing the methanol-modifiedpalladium-tin chloride complex can be utilized as such as an activator.It is also adapted to be mixed together with an aqueous liquid solvent,usually water, and hydrochloric acid prior to use, and it is preferablyso diluted prior to use and typically by mixing together thethus-obtained liquid solution or concentrate, hydrochloric acid, andpurified water in the proportions of 0.5 gallon of HCl (A R grade of 37%HCl concentration) and 4 gallons of the water per gallon of thethus-obtained liquid solution concentrate. Such a diluted activatorsolution gave good results in catalyzing the walls of the through holesof single layer and multi-layer printed circuit boards for subsequentelectroless metal plating at room temperature of the activator solutionand an immersion time in the activator solution of 56 minutes. Thethrough hole walls of both types of boards were electrolessly platedwith a continuous, firmly adherent layer of copper after being catalyzedby immersion in such diluted activator solution.

On the contrary, use of the activator solution containing themethanol-modified noble metal-tin halide complex disclosed and claimedin aforementioned US. Pat. No. 3,767,583 which had been diluted withhydrochloric acid (A R of 37% HCl concentration) and purified water insubstantially identical manner, for catalyzing the through hole walls ofthe single layer and multilayer printed circuit boards resulted inundesirable discontinuousdeposits of copper thereon after theelectroless copper plating.

EXAMPLE 2 The procedure of Example .1 was repeated except thatisopropanol was subsititute'd for methanol in this Example 2. I

The resulting liquid -solution containing the isopropanol-modifiedpalladium-tin chloride complex gives good results, either as such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multi-layer printed circuitboards for electroless metal plating. Electroless copper plating of thethrough hole wall surfaces of both types of circuit boards, which havebeen activated by immersion in the activator solution of this Example 2under substantially the same conditions as in Example 1, results in acontinuous firmly adherent copper deposit on the through hole walls.

EXAMPLE 3 The procedure of Example 1 is repeated except that n-butanolwas substituted for methanol in this Example 3.

The resulting liquid solution containing the nbutanol-modifiedpalladium-tin chloride complex gives good results, either. as such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multiherent copper depositon the through hole walls.

EXAMPLE 6 The procedure of Example 1 is repeated except that aurouschloride (Au Cl) is substituted for palladium chloride in this Example6.

The resulting liquid solution containing the methanol-modified gold-tinchloride complex gives good layer printed circuit boards for electrolessmetal plating. Electroless copper plating of the through hole wallsurfaces of both types of circuit boards, which have been activated byimmersion in the activator solution of this Example 3 undersubstantially thesame conditions as in Example 1, results in acontinuous, firmly adherent copper deposit on the through hole walls.

EXAMPLE 4 The procedure of Example I is repeated except that ethanol issubstituted for methanol in this Example 4.

The resulting liquid solution containing the ethanolmodifiedpalladium-tin chloride complex gives good results, either as' such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multi-layer printed circuitboards for electroless metal plating. Electroless copper plating of thethrough hole wall surfaces of both types of circuit boards, which havebeen activated by immersion in the activator solution of this Example 4under substantially the same conditions as in Example 1, results in acontinuous, firmly adherent copper deposit on the through hole walls.

EXAMPLE 5 The procedure of Example I is repeated except that platinumchloride (Pt Cl is substituted for palladium I chloride in this Example5.

results, either as such as a concentrate or when diluted withhydrochloric acid and water in a similar ratio as is set forth inExample 1 herein, for catalyzing the through hole walls of both singlelayer and multi-layer printed circuit boards for electroless metalplating. Electroless copper plating of the'through hole wall surfaces ofboth types of circuit boards, which have been activated by immersion inthe activator solution of this Example 6 under substantially the sameconditions as in Example 1, results in a continuous, firmly adherentcopper deposit on the through hole walls.

EXAMPLE 7 The procedure of Example 1 is repeated except that platinumchloride (Pt C1 and isopropanol are substituted for palladium chlorideand methanol respectively in this Example 7.

The resulting liquid solution containing the isopropanol-modifiedplatinum-tin chloride complex gives good results, either as such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multilayer printed circuitboards for electroless metal plating. Electroless copper plating ofthethrough hole wall surfaces of both types of circuit boards, which havebeen activated by immersion in the activator solution of this Example 7under substantially the same conditions as in Example 1, results in acontinuous, firmly adherent copper deposit on the through hole walls.

EXAMPLE 8 The procedure of Example 1 is repeated except that platinumchloride (Pt C1 and ethanol are substituted for palladium chloride andmethanol respectively in this Example 8. v

The resulting liquid solution containing the ethanolmodifiedplatinum-tin chloride complex gives good results, either as such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multi-layer- EXAMPLE 9 Theprocedure of Example 1 is repeated except that platinum chloride (PtC12) and n-butanol are substituted for palladium chloride and methanolrespectively in this Example 9.

The resulting liquid solution containing the nbutanol-modifiedplatinum-tin chloride complex gives good results, either as such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multilayer printed boardsfor electroless metal plating. Electroless copper plating of the throughhole wall surfaces of both type of circuit boards, which have beenactivated by immersion in the activator solution of this Example 9 undersubstantially the same conditions as in Example 1, results in acontinuous, firmly adherent copper deposit on the through hole walls.

EXAMPLE 10 The procedure of Example l is repeated except that aurouschloride (Au Cl) and isopropanol are substituted for palladium chlorideand methanol respectively in this Example 10.

The resulting liquid solution containing the iso' propanol-modifiedgold-tin chloride complex gives good results, either as such as aconcentrate or when diluted with hydrochloric acid and water in asimilar ratio as is set forth in Example 1 herein, for catalyzing thethrough hole walls of both single layer and multilayer printed circuitboards for electroless metal plating. Electroless copper plating of thethrough hole wall surfaces of both types of circuit boards, which havebeen activated by immersion in the activator solution of this Example 10under substantially the same conditions as in Example 1, results in acontinuous, firmly adherent copper deposit on the through hole walls.

What is claimed is:

1. A catalyst solution comprising a substantially colloidal metalparticle-free acidic liquid solution containing a soluble loweralkanol-modified noble metal-tin chloride complex, and hydrochloricacid, the soluble lower alkanol-modified noble metal-tin chloridecomplex being obtained by mixing together a lower alkanol, a solublenoble metal chloride, stannous chloride and hydrochloric acid, andmaintaining the thus-obtained liquid mixture at a reaction temperatureof at least about 160F. but below that temperature at which an excessiveamount of noble metal is precipitated for a period sufficient to obtaina catalytically effective solution containing the soluble loweralkanol-modified noble metal-tin chloride complex, the stannous chloridebeing present in excess of the amount thereof required to reduce thenoble metal chloride to zero valent noble metal, the molar ratio ofstannous chloride to noble metal chloride (calculated as palladiumchloride) being initially at least about 9-l0:l respectively, and thelower alkanol being present in amount sufficient to obtain a solublecomplex.

2. The catalyst solution of claim 1 having a pH of less sure build-upina closed container ultimately containing the catalyst solution.

6. The catalyst solution of claim 3 wherein the methanol is added in theformation of the reaction mixture prior to the addition of the noblemetal chloride.

7. The catalyst solution of claim 1 wherein the mixture is maintained atthe temperature of at at least about l'60F. but below that temperatureat which an excessive amount of noble metal is precipitated for a periodof at least about 4-9 hours and sufficient to obtain said solublecomplex.

8. The catalyst solution of claim 1 wherein the mixture is maintained atthe temperature of in the range of about F. to about 185F. for a periodof at least about 9 hours and sufficient to obtain said soluble complex.

9. The catalyst solution of claim 4 wherein the methanol is added in theformation of the reaction mixture prior to the addition of the noblemetal chloride.

10. The catalyst solution of claim 2 wherein the noble metal of thecomplex is palladium and the soluble noble metal chloride is palladiumchloride.

11. The catalyst solution of claim 3 wherein the reaction temperature ismaintained in the range of about F. to about l85 F.

12. The catalyst solution of claim 2 wherein the stannous chloride isadded in increments.

13. The catalyst solution of claim 2 wherein a soluble alkali stannateis mixed together with the lower alkanol, soluble noble metal chloride,stannous chloride and hydrochloric acid. I

14. The catalyst solution of claim 13 wherein the alkali stannate is asoluble alkalimetal stannate.

15. The catalyst solution of claim 14 wherein the alkali metal stannateis sodium stannate.

16. The catalyst solution of claim 2 wherein the soluble loweralkanol-modified noble metal-tin chloride complex is obtained byintroducing water and a soluble alkali metal stannate into a reactionzone, agitating the resulting mixture until the alkali metal stannate isdissolved in the water, adding to the thus-obtained aqueous solution asolution containing stannous chloride and hydrochloric acid, agitatingthe resulting mixture, adding hydrochloric acid to the thus-obtainedmixture, adding a lower alkanol to the thus-obtained mixture, heatingthe resulting mixture to a reaction temperature in the range of about170F. to about C. while agitating said mixture, slowly adding at acontrolled rate a solution of an acid-soluble noble metal chloride inhy' drochloric acid to the thus-obtained mixture, adding to theresulting mixture increments of a solution of stannous chloride inhydrochloric acid, separately adding to the thus-obtained mixturehydrochloric acid and stannous chloride, maintaining the resultingmixture at a reaction temperature in the range of about 170F. to about185F. for a period of at least about 9 hours and sufficient to obtainthe soluble complex, agitating the resulting mixture, and cooling thethus-obtained mixture to room temperature.

17. A method for the preparation of a catalyst solution substantiallyfree of colloidal metal particles which comprises mixing together asoluble noble metal chloride, a lower alkanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature of at least about 160F. but below that temperatureat which an excessive amount of noble metal is precipitated for a periodsufficient to obtain a catalytically effective solution containing thesoluble lower alkanol-modified noble metal-tin chloride complex, thestannous chloride being present in excess of the amount thereof requiredto reduce the noble metal chloride to zero valent noble metal, the molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) being at least about 9-l 0:1 respectively, and thelower alkanol being present in amount sufficient to obtain a solublecomplex.

18. The method of claim 17 wherein the catalytically effective solutionhas a pH less than 1.

19. The method of claim 18 wherein the mixture is maintained at thetemperature of at least about 160F. but below that temperature at whichan excessive amount of noble metal is precipitated for a period of atleast about 4-9 hours and sufficient to obtain said soluble complex.

20. The method of claim 18 wherein the noble metal of the complex ispalladium and the soluble metal chloride is palladium chloride.

21. The method of claim 18 wherein the lower alkanol is methanol.

22. The method of claim 18 wherein the stannous chloride is added inincrements.

23. The method of claim 18 wherein a soluble alkali stannate is mixedtogether with the lower alkanol, solu ble noble metal chloride, stannouschloride and hydrochloric acid.

24. The method of claim 23 wherein the'alkali stannate is a solublealkali metal stannate.

25. The method of claim 24 wherein the alkali metal stannate is sodiumstannate.

26. A method for the preparation of a catalyst solution substantiallyfree of colloidal metal particles which comprises introducing water anda soluble alkali metal stannate into a reaction zone, agitating theresulting mixture until the alkali metal stannate is dissolved in thewater, adding to the thus-obtained aqueous solution a solutioncontaining stannous chloride and hydrochloric acid, agitating theresulting mixture, adding hydrochloric acid to the thus-obtainedmixture, adding a lower alkanol to the thus-obtained mixture, heatingthe resulting mixture to a reaction temperature in the range of about170F. to about 185C. while agitating said mixture, slowly adding at acontrolled rate a solution of an acid-solublenoble metal chloride inhydrochloric acid to the thus-obtained mixture, adding to the resultingixture increments of a solution of stannous chloride in hydrochloricacid, separately adding to the thusobtained mixture hydrochloric acidand a stannous chloride, maintaining the resulting mixture at a reactiontemperature in the range of about 170F. to about 185F. for a period ofat least about 9 hours and sufficient to obtain the soluble complex,agitating the resulting mixture, and cooling the thus-obtained mixtureto room temperature.

27. A catalyst solution comprising a substantially colloidal metalparticle-free acidic liquid solution containing a solublemethanol-modified noble metal-tin chloride complex, and hydrochloricacid, the catalyst solution having a pH of less than 1, the solublemethanolmodified noble metal-tin chloride complex being obtained byintroducing water and a soluble alkali metal stannate into a reactionzone, agitating the resulting mixture until the alkali metal stannate isdissolved in the water, adding to the thus-obtained aqueous solution asolution containing stannous chloride and hydrochloric acid, agitatingthe resulting mixture, adding hydrochloric acid to the thus-obtainedmixture, adding methanol to the thus-obtained mixture, heating theresulting mixture to a reaction temperature in the range of about F. toabout F. while agitating said mixture, slowly adding at a controlledrate a solution of an acidsoluble noble metal chloride in hydrochloricacid to the thus-obtained mixture, adding to the resulting mixtureincrements of a solution of stannous chloride in hydrochloric acid,separately adding to the thus-obtained mixture hydrochloric acid andstannous chloride, maintaining the resulting mixture at a reactiontemperature in the range of about 170F. to about 185F. for a period ofat least about 9 hours and sufficient to obtain the soluble complex,agitating the resulting mixture, and cooling the thus-obtained mixtureto room temperature, the stannous chloride being present in excess ofthe amount thereof required to reduce the noble metal chloride to zerovalent noble metal, the molar ratio of stannous chloride to noble metalchloride (calculated as palladium chloride) being initially at leastabout 9lO:l respectively, and the methanol being present in amountsufficient to obtain a soluble complex.

28. The catalyst solution of claim 27 wherein the noble metal ispalladium, the noble metal chloride is palladium chloride, the alkalimetal stannate is sodium stannate, and the cooling of the thus-obtainedmixture is by permitting said mixture to cool to room temperaturewithout agitation of the mixture, and thereafter agitating thethus-obtained solution for at least 15 minutes.

29. A method for the preparation of a catalyst solution substantiallyfree of colloidal metal particles which comprises mixing together asoluble noble metal chloride, methanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature in the range of about 160F. to about 185F. for aperiod sufficient to obtain a catalytically effective solutioncontaining the soluble methanol-modified noble metal-tin chloridecomplex, the stannous chloride being present in excess of the amountthereof required to reduce the noble metal chloride to zero valent noblemetal, the molar ratio of stannous chloride to noble metal chloride(calculated as palladium chloride) being at least 9-l0zl respectively,and the methanol being present in amount sufficient to obtain a solublecomplex.

30. The method of claim 29 wherein the methanol is present in amountsufficient to obtain a soluble complex but insufficient to result inexcessive by-product formation with attendant excessive gas pressurebuildup in a closed container ultimately containing the catalystsolution.

31. The method of claim 29 wherein the methanol is added in theformation of the reaction mixture prior to the addition of the noblemetal chloride.

32. A method for the preparation of a catalyst solu- I tionsubstantially free of colloidal metal particles which comprises mixingtogether a soluble noble metal chloride, methanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature in the range of about 160F. to about 185F. for aperiod of at least about 9 hours and sufficient to obtain acatalytically effective solution containing the solublemethanol-modified noble metaltin chloride complex, the stannous chloridebeing present in excess of the amount thereof required to reduce thenoble metal chloride to zero valent noble metal, the molar ratio ofstannous chloride to noble metal chloride (calculated as palladiumchloride) being at least about 9-1011 respectively, and the methanolbeing present in amount sufficient to obtain a soluble complex, thecatalytically effective solution having a pH less than 1.

33. A method for the preparation of a catalyst solution substantiallyfree of colloidal metal particles which comprises mixing together asoluble noble metal chloride, methanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature in the range of about 160F. to about 185F. for aperiod sufficient to obtain a catalytically effective solutioncontaining the soluble methanaol-modified noble metal-tin chloridecomplex, the methanol being added in the formation of the mixture priorto the addition of the noble metal chloride, the stannous chloride beingpresent in excess of the amount thereof required to reduce the noblemetal chloride to zero valent noble metal, the molar ratio of stannouschloride to noble metal chloride (calculated as palladium chloride)being at least about 9l0:1 respectively, and the methanol being presentin amount sufficient to obtain a soluble complex.

34. A method for the preparation of a catalyst solutiton substantiallyfree of colloidal metal particles which comprises mixing together asoluble noble metal chloride, methanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature in the range of about l'70F. to

about 185F. for a period sufficient to, obtain a catalytically effectivesolution containing the soluble methanol-modified noble metal-tinchloride complex, the stannous chloride being present in excess of theamount thereof required to reduce the noble metal chloride to zerovalent noble metal, the molar ratio of stannous chloride to noble metalchloride (calculated as palladium chloride) being at least about 9-1011respectively, and the lower alkanol being present in amount sufficientto obtain a soluble complex, the catalytically effective solution havinga pH less than 1.

35. A method for the preparation of a catalyst solution substantiallyfree of colloidal metal particles which comprises introducing water anda soluble alkali metal stannate into a reaction zone, agitating theresulting mixture until the alkali metal stannate is dissolved in thewater, adding to the thus-obtained aqueous solution a solutioncontaining stannous chloride and hydrochloric acid, agitating theresulting mixture, adding hydrochloric acid to the thus-obtainedmixture, adding methanol to the thus-obtained mixture, heating theresulting mixture to a reaction temperature in the range of about F. toabout C. while agitating said mixture, slowly adding at a controlledrate a solution of an acidsoluble noble metal chloride in hydrochloricacid to the thus-obtained mixture, adding to the resulting mixtureincrements of a solution of stannous chloride in hydrochloric acid,separately adding to the thus-obtained mixture hydrochloric acid and astannous chloride, maintaining the resulting mixture at a reactiontemperature in the range of about 170F. to about 185F. for a period ofat least about 9 hours and sufficient to obtain the soluble complex,agitating the resulting mixture, and cooling the thus-obtained mixtureto room UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,871,889 Dated March 18, 1975 Inventor(s) Earl J. Fadgen, et al It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Page 1, line 5 of ABSTRACT, "alkanolmodified" should readalkanol-modified Column 1, line 37, "system" should read systems line66, "plated should read plating Coluun 2-, line 35, catlyzing shouldread catalyzing Column 3, line 9, "Excessive' should read excessiveline17, "'hydorchloric" should read hydrochloric Colunmi i', line 65,"dillution" should read dilution Colum 5, line 45,-

-- iridium, e.g. iridium Column 6, line 47', "hydorchlo'ric" should readhydrochloric Column 7, line 41, 1itn3" should read lting line 42, lshould be inserted after "pH" and before *during".- Column 8, 'line 56,with a should be in.- serted after surfaces and before the come. Colurm9, line'59, "ele'cotro" should read electro line 62, "100" should read200 Column 13, line 9, -circuit should be inserted after- "printed" andbefore "boards"; line 11, "type should read types Colum 17, 'line 28,,"ton" should be changed to "9 Signed and Scaled this Thirty-first Day OfOctober 1978 [SEAL] Attest:

RUTH MASON DONALD w. BANNER Arresting Oflicer C'ommissiour of Patentssud Trademarks "irridium" should be deleted and. the followingsubstituted jherefor

1. A CATALYST SOLUTION COMPRISING A SUBSTANTIALLY COLLOIDAL METALPARTICLE-FREE ACIDIC LIQUID SOLUTION CONTAINING A SOLUBLE LOWERALKANOL-MODIFIED NOBLE METAL-TIN CHLORIDE COMPLEX, AND HYDROCHLORICACID, THE SOLUBLE LOWER ALKANOL-MODIFIED NOBLE METAL-TIN CHLORIDECOMPLEX BEING OBTAINED BY MIXING TOGETHER A LOWER ALKANOL, A SOLUBLENOBLE METAL CHLORIDE, STANNOUS CHLORIDE AND HYDROCHLORIC ACID, ANDMAINTAINING THE THUSOBTAINED LIQUID MIXTURE AT A REACTION TEMPERATURE OFA LEAST ABOUT 160*F. BUT BELOW THAT TEMPERATURE AT WHICH AN EXCESSIVEAMOUNT OF NOBLE METAL IS PRECIPITATED FOR A PERIOD SUFFICIENT TO OBTAINA CATALYTICALLY EFFECTIVE SOLUTION CONTAINING THE SOLUBLE LOWERALKANOL-MODIFIED NOBLE METAL-TIN CHLORIDE COMPLEX, THE STANNOUS CHLORIDEBEING PRESENT IN EXCESS OF THE AMOUNT THEREOF REQUIRED TO REDUCE THENOBLE METAL CHLORIDE TO ZERO VALENT NOBLE METAL, THE MOLAR RATIO OFSTANNOUS CHLORIDE TO NOBLE METAL CHLORIDE (CALCULATED AS PALLADIUMCHLORIDE) BEING INITIALLY AT LEAST ABOUT 9-10:1 RESPECTIVELY, AND THELOWER ALKANOL BEING PRESENT IN AMOUNT SUFFICIENT TO OBTAIN A SOLUBLECOMPLEX.
 2. The catalyst solution of claim 1 having a pH of less than 1.3. The catalyst solution of claim 2 wherein the lower alkanol ismethanol.
 4. The catalyst solution of claim 3 wherein the reactiontemperature is maintained in the range of about 160*F. to about 185*F.5. The catalyst solution of claim 3 wherein the methanol is present inamount sufficient to obtain a soluble complex but insufficient to resultin excessive by-product formation with attendant excessive gas pressurebuild-up in a closed container ultimately containing the catalystsolution.
 6. The catalyst solution of claim 3 wherein the methanol isadded in the formation of the reaction mixture prior to the addition ofthe noble metal chloride.
 7. The catalyst solution of claim 1 whereinthe mixture is maintained at the temperature of at at least about 160*F.but below that temperature at which an excessive amount of noble metalis precipitated for a period of at least about 4-9 hours and sufficientto obtain said soluble complex.
 8. The catalyst solution of claim 1wherein the mixture is maintained at the temperature of in the range ofabout 160*F. to about 185*F. for a period of at least about 9 hours andsufficient to obtain said soluble complex.
 9. The catalyst solution ofclaim 4 wherein the methanol is added in the formation of the reactionmixture prior to the addition of the noble metal chloride.
 10. Thecatalyst solution of claim 2 wherein the noble metal of the complex ispalladium and the soluble noble metal chloride is palladium chloride.11. The catalyst solution of claim 3 wherein the reaction temperature ismaintained in the range of about 170*F. to about 185*F.
 12. The catalystsolution of claim 2 wherein the stannous chloride is added inincrements.
 13. The catalyst solution of claim 2 wherein a solublealkali stannate is mixed together with the lower alkanol, soluble noblemetal chloride, stannous chloride and hydrochloric acid.
 14. Thecatalyst solution of claim 13 wherein the alkali stannate is a solublealkali metal stannate.
 15. The catalyst solution of claim 14 wherein thealkali metal stannate is sodium stannate.
 16. The catalyst solution ofclaim 2 wherein the soluble lower alkanol-modified noble metal-tinchloride complex is obtained by introducing water and a soluble alkalimetal stannate into a reaction zone, agitating the resulting mixtureuntil the alkali metal stannate is dissolved in the water, adding to thethus-obtained aqueous solution a solution containing stannous chlorideand hydrochloric acid, agitating the resulting mixture, addinghydrochloric acid to the thus-obtained mixture, adding a lower alkanolto the thus-obtained mixture, heating the resulting mixture to areaction temperature in the range of about 170*F. to about 185*C. whileagitating said mixture, slowly adding at a controlled rate a solution ofan acid-soluble noble metal chloride in hydrochloric acid to thethus-obtained mixture, adding to the resulting mixture increments of asolution of stannous chloride in hydrochloric acid, separately adding tothe thus-obtained mixture hydrochloric acid and stannous chloride,maintaining the resulting mixture at a reaction temperature in the rangeof about 170*F. to about 185*F. for a period of at least about 9 hoursand sufficient to obtain the soluble complex, agitating the resultingmixture, and cooling the thus-obtained mixture to room temperature. 17.A method for the preparation of a catalyst solution substantially freeof colloidal metal particles which comprises mixing together a solublenoble metal chloride, a lower alkanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature of at least about 160*F. but below that temperatureat which an excessive amount of noble metal is precipitated for a periodsufficient to obtain a catalytically effective solution containing thesoluble lower alkanol-modified noble metal-tin chloride complex, thestannous chloride being present in excess of the amount thereof requiredto reduce the noble metal chloride to zero valent noble metal, the molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) being at least about 9-10:1 respectively, and thelower alkanol being present in amount sufficient to obtain a solublecomplex.
 18. The method of claim 17 wherein the catalytically effectivesolution has a pH less than
 1. 19. The method of claim 18 wherein themixture is maintained at the temperature of at least about 160*F. butbelow that temperature at which an excessive amount of noble metal isprecipitated for a period of at least about 4-9 hours and sufficient toobtain said soluble complex.
 20. The method of claim 18 wherein thenoble metal of the complex is palladium and the soluble metal chlorideis palladium chloride.
 21. The method of claim 18 wherein the loweralkanol is methanol.
 22. The method of claim 18 wherein the stannouschloride is added in increments.
 23. The method of claim 18 wherein asoluble alkali stannate is mixed together with the lower alkanol,soluble noble metal chloride, stannous chloride and hydrochloric acid.24. The method of claim 23 wherein the alkali stannate is a solublealkali metal stannate.
 25. The method of claim 24 wherein the alkalimetal stannate is sodium stannate.
 26. A method for the preparation of acatalyst solution substantially free of colloidal metal particles whichcomprises introducing water and a soluble alkali metal stannate into areaction zone, agitating the resulting mixture until the alkali metalstannate is dissolved in the water, adding to the thus-obtained aqueoussolution a solution containing stannous chloride and hydrochloric acid,agitating the resulting mixture, adding hydrochloric acid to thethus-obtained mixture, adding a lower alkanol to the thus-obtainedmixture, heating the resulting mixture to a reaction temperature in therange of about 170*F. to about 185*C. while agitating said mixture,slowly adding at a controlled rate a solution of an acid-soluble noblemetal chloride in hydrochloric acid to the thus-obtained mixture, addingto the resulting mixture increments of a solution of stannous chloridein hydrochloric acid, separately adding to the thus-obtained mixturehydrochloric acid and a stannous chloride, maintaining the resultingmixture at a reaction temperature in the range of about 170*F. to about185*F. for a period of at least about 9 hours and sufficient to obtainthe soluble complex, agitating the resulting mixture, and cooling thethus-obtained mixture to room temperature.
 27. A catalyst solutioncomprising a substantially colloidal metal particle-free acidic liquidsolution containing a soluble methanol-modified noble metal-tin chloridecomplex, and hydrochloric acid, the catalyst solution having a pH ofless than 1, the soluble methanol-modified noble metal-tin chloridecomplex being obtained by introducing water and a soluble alkali metalstannate into a reaction zone, agitating the resulting mixture until thealkali metal stannate is dissolved in the water, adding to thethus-obtained aqueous solution a solution containIng stannous chlorideand hydrochloric acid, agitating the resulting mixture, addinghydrochloric acid to the thus-obtained mixture, adding methanol to thethus-obtained mixture, heating the resulting mixture to a reactiontemperature in the range of about 170*F. to about 185*F. while agitatingsaid mixture, slowly adding at a controlled rate a solution of anacid-soluble noble metal chloride in hydrochloric acid to thethus-obtained mixture, adding to the resulting mixture increments of asolution of stannous chloride in hydrochloric acid, separately adding tothe thus-obtained mixture hydrochloric acid and stannous chloride,maintaining the resulting mixture at a reaction temperature in the rangeof about 170*F. to about 185*F. for a period of at least about 9 hoursand sufficient to obtain the soluble complex, agitating the resultingmixture, and cooling the thus-obtained mixture to room temperature, thestannous chloride being present in excess of the amount thereof requiredto reduce the noble metal chloride to zero valent noble metal, the molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) being initially at least about 9-10:1 respectively,and the methanol being present in amount sufficient to obtain a solublecomplex.
 28. The catalyst solution of claim 27 wherein the noble metalis palladium, the noble metal chloride is palladium chloride, the alkalimetal stannate is sodium stannate, and the cooling of the thus-obtainedmixture is by permitting said mixture to cool to room temperaturewithout agitation of the mixture, and thereafter agitating thethus-obtained solution for at least 15 minutes.
 29. A method for thepreparation of a catalyst solution substantially free of colloidal metalparticles which comprises mixing together a soluble noble metalchloride, methanol, stannous chloride and hydrochloric acid, andmaintaining the thus-obtained mixture at a reaction temperature in therange of about 160*F. to about 185*F. for a period sufficient to obtaina catalytically effective solution containing the solublemethanol-modified noble metal-tin chloride complex, the stannouschloride being present in excess of the amount thereof required toreduce the noble metal chloride to zero valent noble metal, the molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) being at least 9-10:1 respectively, and the methanolbeing present in amount sufficient to obtain a soluble complex.
 30. Themethod of claim 29 wherein the methanol is present in amount sufficientto obtain a soluble complex but insufficient to result in excessiveby-product formation with attendant excessive gas pressure build-up in aclosed container ultimately containing the catalyst solution.
 31. Themethod of claim 29 wherein the methanol is added in the formation of thereaction mixture prior to the addition of the noble metal chloride. 32.A method for the preparation of a catalyst solution substantially freeof colloidal metal particles which comprises mixing together a solublenoble metal chloride, methanol, stannous chloride and hydrochloric acid,and maintaining the thus-obtained mixture at a reaction temperature inthe range of about 160*F. to about 185*F. for a period of at least about9 hours and sufficient to obtain a catalytically effective solutioncontaining the soluble methanol-modified noble metal-tin chloridecomplex, the stannous chloride being present in excess of the amountthereof required to reduce the noble metal chloride to zero valent noblemetal, the molar ratio of stannous chloride to noble metal chloride(calculated as palladium chloride) being at least about 9-10:1respectively, and the methanol being present in amount sufficient toobtain a soluble complex, the catalytically effective solution having apH less than
 1. 33. A method for the Preparation of a catalyst solutionsubstantially free of colloidal metal particles which comprises mixingtogether a soluble noble metal chloride, methanol, stannous chloride andhydrochloric acid, and maintaining the thus-obtained mixture at areaction temperature in the range of about 160*F. to about 185*F. for aperiod sufficient to obtain a catalytically effective solutioncontaining the soluble methanaol-modified noble metal-tin chloridecomplex, the methanol being added in the formation of the mixture priorto the addition of the noble metal chloride, the stannous chloride beingpresent in excess of the amount thereof required to reduce the noblemetal chloride to zero valent noble metal, the molar ratio of stannouschloride to noble metal chloride (calculated as palladium chloride)being at least about 9-10:1 respectively, and the methanol being presentin amount sufficient to obtain a soluble complex.
 34. A method for thepreparation of a catalyst solutiton substantially free of colloidalmetal particles which comprises mixing together a soluble noble metalchloride, methanol, stannous chloride and hydrochloric acid, andmaintaining the thus-obtained mixture at a reaction temperature in therange of about 170*F. to about 185*F. for a period sufficient to obtaina catalytically effective solution containing the solublemethanol-modified noble metal-tin chloride complex, the stannouschloride being present in excess of the amount thereof required toreduce the noble metal chloride to zero valent noble metal, the molarratio of stannous chloride to noble metal chloride (calculated aspalladium chloride) being at least about 9-10:1 respectively, and thelower alkanol being present in amount sufficient to obtain a solublecomplex, the catalytically effective solution having a pH less than 1.35. A method for the preparation of a catalyst solution substantiallyfree of colloidal metal particles which comprises introducing water anda soluble alkali metal stannate into a reaction zone, agitating theresulting mixture until the alkali metal stannate is dissolved in thewater, adding to the thus-obtained aqueous solution a solutioncontaining stannous chloride and hydrochloric acid, agitating theresulting mixture, adding hydrochloric acid to the thus-obtainedmixture, adding methanol to the thus-obtained mixture, heating theresulting mixture to a reaction temperature in the range of about 170*F.to about 185*C. while agitating said mixture, slowly adding at acontrolled rate a solution of an acid-soluble noble metal chloride inhydrochloric acid to the thus-obtained mixture, adding to the resultingmixture increments of a solution of stannous chloride in hydrochloricacid, separately adding to the thus-obtained mixture hydrochloric acidand a stannous chloride, maintaining the resulting mixture at a reactiontemperature in the range of about 170*F. to about 185*F. for a period ofat least about 9 hours and sufficient to obtain the soluble complex,agitating the resulting mixture, and cooling the thus-obtained mixtureto room temperature.